Since always, laminates used for printed circuit usually adopt a halogen flame retardant to prevent burning, particularly adopt tetrabromobisphenol-A epoxy resin. This brominated epoxy resin has good flame retardancy, but it will produce hydrogen bromide gas when burning. Besides, in recent years, carcinogens, such as dioxin and dibenzofuran, are detected in the combustion products of waste electrical and electronic equipments containing halogens such as chlorine and bromine. So, the application of brominated epoxy resins is limited.
With the EU directives on WEEE (Waste Electrical and Electronic Equipment) and RoHS (Restriction of Hazardous Substances in Electrical and Electronic Equipment) being put into practice in Jul. 1, 2006, developing halogen-free and flame-retardant laminates used in printed circuits has become the key work of the industry.
On the other hand, with the lead-free times coming, for a printed circuit board, besides the halogen-free flame retardant property, the function of being compatible with lead-free soldering also becomes important. So, laminates used for printed circuit also require more thermal resistance and reliability than ever before.
To solve the above mentioned problems, the Chinese patent No. ZL200410051855.3 disclosed a resin composition that adopts phosphorus-containing epoxy resin and bisphenol-A benzoxazine resin as the base resin. The cured resin has high glass transition temperature (Tg), high thermal resistance, low dielectric dissipation factor, low C.T.E, and good flame retardancy. But, since the base resin is phosphorus-containing epoxy resin and bisphenol-A benzoxazine resin, the cured resin is comparatively brittle, and has general processability, low flexural strength and comparatively poor chemical resistance.
And, the Chinese patent No. ZL02803484.8 disclosed a resin composition that adopts bisphenol-F benzoxazine resin and bisphenol-F epoxy resin as the base resin. The cured resin has high glass transition temperature (Tg), high thermal resistance, high modulus of elasticity, low dielectric dissipation factor, good flame retardancy, and good processability. But, since a condensed phosphate type flame retardant is added to the resin composition, the chemical resistance and anti-CAF property of the cured resin can not be guaranteed, that is, the long term reliability is under great risk.
Besides, the Chinese patent No. ZL01814589.2 disclosed an epoxy resin composition of halogen-free flame retardant type that adopts a phenoxyphosphazene compound. The laminates used for printed circuit that use the resin composition have good thermal resistance, low moisture and good flame retardancy. Comparing the above mentioned phenoxyphosphazene flame retardant with common phosphorus-containing flame retardants (such as condensed phosphate), it can be dissolved in an organic solvent, and be easily evenly distributed in a resin composition. And, it has the advantages such as having a comparatively high thermal decomposition temperature, having low moisture, and being hard to hydrolyze. But, since the base resin of the resin composition in the patent is an ordinary epoxy resin and phenolic resin, which does not have flame retardancy itself, plenty of phenoxyphosphazene compound (about 23-31 wt %) must be added to it in order to impart enough flame retardancy. If the laminates are at high temperature condition, the phenoxyphosphazene compound may migrate or even bleed out, and the physical properties such as flexural strength will fall off sharply.